Frictional holding device for use in wells



Feb. 24, 1959 yM. w. HAlNEs FRICTIONAL HOLDING DEVICE FOR USE IN WELLS Filed July '26, 1954 JNVENTOR. ,A4/:e605 W. H1/N55,

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United `States Patent@ anvar/as.4 FRlc'rIoNALHoLlnStGDEvI-CE FOR USE- INWELLS Y Mar'cusV WHanesyIrzogBeach, Calif. Appliafinralzt, 19.54; serial Np. 445,729 afl-claims (cli 16mm This; invention l' relates@ tot akfrictionalY holding device for usein.y connectionwith thelftubingstringuin wells, particularly oil wells.

It is-one object:k of thisinventiomtoprovidefor releasably anchoring a tubing string in a-v'vellthroughthe medium of. anchoring: members-whichwwithout biting-,into-or penetratingthe surfacelsof the well casing or a tubular part of av tool. positionedv in-V the well, andsolely by frictional contact with the casingzor such tubular part, will restrain` axial movementofI the ltubing string relative to the casing or such tubular member. Y

It is anotherfobject ofxthisinvention to providetan'ovel and'highly` ecientmethod, of -frictionally,restraining axial movement oi? the tulningstring'4 in awell and of` providing for axialj movement; of the/tubing string-whenlforces developed ini orappledgto the -stringand tending to move the String axially; overcome. the frictional restraining force.

It is another objectgtoiproyide ajdevice-Lo the character described, /whereinlholdingrnembers are urged by. the pressure,A of `lluid Yinfthe tubing; string-finto vfrictional engagement with-a tubular-member in`v the well` to releasably hold the stringandtubularfmember against relative axial movement;` n Y In accordance fwith-thisinvention .fluid pressure actuated anchoring members;-havinggsubstantially smooth anchoring surfaces are employed insteadofthe conventional` toothed onrougl'iened surfaces which tend to bite-into and interlock, withy thev casing; yThese substantially smooth anchoring` surfaces make itv possibleto restrainl axial movement-ofthe tubing jdstring solely lby friction, but,

permit the-tubing stringito mjove axiallyewithout damaging the string or casing, vflhenfav force kdeveloped in or` applied to the string, and.v tending to move it axially, overcomes the frictional holding .orcegof the anchoring. mem-v bers.

In, tubing .anchors .of thetype 4employing uid pressureactuated anchorin'gtmembers having toothed or serrated casingfcontacting surfaces, such members sometimes become lockedin thefwell.""'Accordinglmeans areusually provided for relieving` the" Huid pressure holding the anchoring members in` anchoring engagement with the casing, in order that the. tubing.V string. and anchoring means maybe moved axially withoutdamaging thestring, casing and/or4 the anchors. The means for relieving the uid presseon suchfaiianchor is costly and the use thereof hazard-ous as it entailsthe lowering of a tool in the Well or the manipulation `of: ther tubing string to actuate valve means4A for relieving vlthe' `pressureinto the l casing annulus.

Accordingly, itis another object. of Athis invention to provide a fluid pressure-energized tubing anchor which makes it unnecessaryl to employpressureV bleeding or pressure relievngmeans torel'ea'se the tubing for vaxial-movernent in the well. p. A

It is an additional Ob'ct of, this'inven'tionto provide a tubing anchor, such "as cri'bed, for releasablyf restraining axial movement ofyaireciprcating pump andthe tub- 2,8%,783 Patented 24,A

2 ing string to Vwhich the'pump is attached, by the use'fof anchoring members mounted lontlie tubingistring` and had!` ing smoothcasing-contacting surfaces urgedaga'inst the casing responsive to uidpressures Vdevelopwedin'thetubing string during operationbf the-pump." t Y I.

It: islanother object` hereof to providet bing anchoring means wherein casing gripping members, such'fVas-5de# scribed, are urged to friction'ally gripthe ca-singfbyemeans ofv pistonand-'cylinder units; proportioned'aiid arr "ged according tothe idpress'ures which'aiedevelopediiria tubing stringof given cross', sectional area-lV Withl arran'ge'rrient,`A` the Vanchoring members are -r'g'edtiixto fricf tional contact withfthe casing undera forcesuzicierit-fto restrainaxial= movementl of the tubing"strin'g," but?y ill Arelease the tubing string when a force developed in or applied to the string and tending ,to move thesti'itig Y axially, overcomesthev frictional holding force4 of the anchoring -`members; n i

Another object of this invention i-s-,to provide ailc'lior-` ing means, such as described, wherein-elongatedfmern'bers may be employed to advantage as the'anchorin'gl `rn`e1 I 1.-fl bers having smooth casing engaging surfaces, inasmuch assuchmembers will facilitate the loweringv andi-raising of the string in Vthe -well casing.

rThisinvention possesses many other advantages'and has other objects which may-'be made more easily apparent from a consideration-"oftwo'embodimentsfofthe-in# vention. For this purpose there lare shown forms in the drawings accompanying and forming part of# the present ispecication; These lforms will now be Vdescribed in detail,`illustrating the general principles of'thefinvention; but it isA to be understood that this -detailed descrip tionis not .to betaken-in-a limitingA sense, since the` scope of the finvention is` best defined by the appended-claime- Referring to the drawings;

i Fig.' l1V is` afragrnentar'ly vertical=sectionalfwiewof^-a typical producing well'wherein th'etubing string is-lprol vided with uidV pressure actuatedanchoring meansfembodying the presentinvention;

Fig. 2`is an enlargedelevational-sectionalview; partly in elevation, of the anehoringmeans shown*iIFigJk Fig; 3 is a-sectio'nal view kvtaken-"on theline*S14-35''ofiFigf invention. Thepump 2,herevshown-,`1is of thereciprqeatiA ing type havingthe usual plunger- P, standing valve VI and travelling valve Wand being operated byfthe'usual sucker rod string R;

The anchoring means generallyV comprises a `plural-ityl` of anchoring members 4 mounted on the exteriorfoffthe tubing string l'for lateral'movement yinto` fifictiorialv` contact with the casing, Each of these anchoring members is provided with 'a casing-'contacting surface'S` which Vis contoured in `accordance with the casing wall'and "urged"v to frictionally contact the casingv 3n byl iluidi pressu'refactuated means 6 carried by the tubing string;

The casing-contacting surfacesv 5, of the members. 4-

are formed so as to restrain axial movement; ofthe tubing solely by frictional contact with lthe casingancl-*will'` not bite into or penetrate thesurface ofgthe; casing as'=is the case withkconyentional toothed or serratedslipsi; Ac-fi I cordingly, the surfaces 5A are preferably-,1substantially smooth so that the members 4 may slide axially while in cntact'with the casing when forces applied to or developed in the tubing string and tending to move the string axially, exceed the frictional holding force developed by ud pressure during pumping of the well.

The anchoring members 4 and the fluid pressure actuated means 6 are constructed, proportioned and ar'- ranged iniconsideration of the inside diameter of the tubing `string and the fluid pressure developed therein under pumping operations, so that the fluid pressure will cause the anchoring members to effect and maintain a frictional contact with the casing sucient to restrain axial movement of the pump and adjacent portion of the-tubing string-during pumping operations. A 1 A tubing` anchor embodying the present invention will permit the tubing string to hang in natural repose under the total loadthereon, but will restrain by frictionl alone, axalmovement of .the pumpand tubing string during operationof *the pump. i The anchor readily may be set'and reset as desired by'manipulation of the tubing string from the surface and will be automatically released and reset responsive to expansion or contraction of the tubing string and responsive to the uid pressure developed in the string, respectively. Thus, it is seen that the anchor provides for an automatic compensation of destructive tubing stretch or contraction such as may be caused byY temperature changes in the well, varying differential fluid levels between the interior of the tubing and the casing annulus, gas to oil ratio changes, and similarly developed forces.

The anchoring members 4 may be of any suitable form having smooth casing-engaging surfaces, provided they are movable laterally under pressure of Huid in the tubing string to cause the smooth surfaces to frictionally engage the casing and restrain movement of the tubing string, and willslide and permit ofv axial movement of the tubing string in the casing when a force developed in or applied to the string and tending to move the string axially, becomes vgreater than the uid-pressure-efected frictional holding `force of the anchoring members.

I r the'present embodiment of this invention each of the anchoring members 4 is in the form ofra bowed leaf spring or similar ilexible member. The smooth and contoured casing-engaging surface of each of the anchoring members is provided on the exterior of a comparatively straight elongated portion 7 intermediate the ends of each anchoring member.

Ashere shown, three of the anchoring members 4 are mounted on the exterior of a sectional tubular body 8. The body 8 consists of two end sections 8a and 8b `threadedly connected to the ends of an intermediate section 8c. The body 8 is connected in the tubing string above the pump 2. The three anchoring members'4 are angularly spaced about the axis of the body 8 andextend longitudinally thereof, being here shown as equidistantlv spaced. Asa means for mounting the anchoring members 4 on the body 8, the upper ends 9 thereof may be hooked and xedly engaged in slots 10 formed in retaining blocks 11 welded tothe end sectionrSa of the body. Housings 12 having beveled upper ends 13 are removably secured by screws 14, as shown in Fig. 2, to the blocks 11 so as to cover-the ends 9 and retain them in engagement with the blocks 11.

The lower hooked ends 15 of the members 4, as shown in-Fig. 2, may be slidably retained on the section 8b of the body 8 by means of blocks 16 and removable housings-17 ;similar to the blocks 11 and housings 12. The lower ends ofthe blocks 16 and the closed ends of the housings 17 serve as stops to limit the sliding movement of the lower ends 15 of the members 4. The removable housings 12 and 17 provide for readily replacing the anchoring members 4. f

The uid-pressure-operated means for operating" each Y anchoring-member 4, as here shown,rinc'ludes a pair of cylinders v18"'fo'rined one above theother in an enlarge# associated anchoring member 4.

The pistons 21, having sealing rings 23 thereon, are slidably held in place in the cylinders 18 by means of pins 24 which are press-fitted in. openings 25 in the cylinders and extend through longitudinal slots 26 in the pistons. These slots permit limited outward movement of the pistons. The pins 24 may be removed to permit the removal and replacement of the pistons.

At their inner ends, the bores of the cylinders 18 are tapered convergently, as at 27, to prevent accumulations of sand and other foreign matter in the cylinders and consequent possible freezing of the pistons in the cylinders.

Set screws 28 may be employed to hold the threadedly coupled sections 8a, 8b and 8c of the body 8 in coupled relation. The sectional formation of the body reduces the cost of the tool and facilitates the assembling and disassembling thereof. It also makes it possible readily to substitute pistons of requisite length as well as the anchoring members 4 when such substitution may be dcsired.

While in the present embodiment of this invention two pistons 21 are provided for urging each member 4 into frictional contact with the casing, it is to be understood that additional pistons may be used, if desired, to provide for the proper frictionalholding force in consideration of the diameter of the tubing string with which the anchor is used.

It has been found that if the total area of the portions of the pistons 21 exposed to the fluid pressure within the tubing string, is between ve and six and one-half times the average internal cross sectional area of the tubing string, theeifective' fluid pressure developed in the tubing string during operation of the pump will cause the anchoring members to frictionallyengagethe casing with a force sufcient to restrainV axial movement of the pump and the tubing string. v

With the foresaid ratio established in an anchor made in accordance with this invention and installed in the tubing string of a yproducing well operated by a reciprocating pump, the frictional engagement of the anchoring members with the casing is sucient to restrain axial movement of the string, by reason of the fluid pressure effective against the pistons 21 during the reciprocation of the pumpplunger,v therebyy preventing downward stretching movement or upward contracting movement of the tubing string during such operation of the pump. The consideration of the depth'at'which the pump is operated, also the viscosityV and gravity of the oil within practicable limits, is of no, appreciable consequence, as the anchoring action will be automatically proportionally adequate at various depths in view of the aforesaid ratio.

However, when a force tending to move the string axially, or when it is desired to lift or move the string axially by a force applied at the surface, and these forces overcome the uid-pressure-effected t frictional holding force of ythe anchoring members, the latter will slide axially of the casing and thereby permit of axial movement of the string without said forces damaging the tubing string or: the casing. Y

It will now be apparent that the present invention provides a novel and highly eicient method of anchoring the tubingtstring 4of. a producing ywell against axial movement during the pumping operation. This method includes the steps ofv positioning in the well casing the tubing string, the anchoringmembers and the pump, and thenjurging the anchoring members intoffrictional contact with the casing *underl a force developed from fluid pressure responsive means,having ,an area'` sufficiently greater than the internalcrossfsectionaljareal of' the tubing' string to cause the anchoring members to frictionally Varichorivngmember, thereby relieving the string Vof excessiveloads and'preventingdamage' to the string and the casing.

Asshown `in Fig; 5, a modified form. off this. invention contemplates the use ofja plurality of, pistons as the anchoringlmembers, wherein the pistons have smooth anchoring surfaces., "l f Accordingly, a tubular body 30,' similar to the body shownin. Figs. 1-4, is mounted lin the tubing string and provided withf.cylind ers 311andpstons' 32 corresponding tothe cylinders and pistons show'ninY Figs. 1-4, except tl'ratvthe pistonshave smooth casing-contactingsurfaces 32a.Y These, pistons may be retained in the cylinders by means of pins S13-.extending through the cylinders and 'slots 34 inthe pistonsin substantially the same manner as shown in Figs. 1 4. Y

The smooth surfaces 32a ofthe pistons 32are shown as`contoured to conform to the curvature of the casing 35 and to facilitate movement of." the pistons past the joints in the casing` stringl Obviously, the smooth surfacesmay be integral with the. pistons or provided on separate members ,fixedtothe ends` ofthe piston.

Any suitable `number of Vthepistons angularly spaced about the axis ofthebody `30, and, if desired, equidistantly spaced from one another, may be employed to provide the desired total piston area exposed to iiuid pressure in the stringas against the average internal cross section area of the tubing string and body 30, whichiatter-in effect is apart ofthe string. Forexample, thetotal areaoffthe,pistons ex'posedtothe Huid pressure in the string, may be between fveandsix and one-half times the .averagefinternalfcross sectional areay ofl the tubing string. It should be noted that. a tubing anchor embodyingthe present invention is` not limited to use with'the tubing strings ofhreciprocating pumps, asitmay be used to anchor tubing strings employedwith well tools in-the operation of which..tiuid\V pressures are developed in the tubing strings,- or with .a string where `it is desired tojanchorithe `latter,toaftubular member which is `to be withdrawn `from or repositioned in a well.

Whetherl the anchoring meansof this invention is employed to anchoratubing string to a well casingor to engage a.tubular member'in awellfso as to'restrain relative Vmoven1entbetween A thev tubingstring and such `tubular member, the frictionalholding..force of` the. anchoring -means will be. sufficient to-achieve! the .purposes hereinbefore, noted. However, should a force ,tending t'o move the tubingstringgaxiallyrelative to thecasing or tubular member and `exceeding the. frictional holding force ofthe anchoringrmeans, be -applied intentionally to or unintentionally developedV in` the tubing string, the smooth surfaces `of the. anchoringimeans will slide freely relative torthe casingor tubular member so as torprevent damage of the tubing string, casing ortubular member.-

l. An anchor for releasably restraining axial movementlof a tubing' string'` in a well, comprising:l anchoring members mounted on` the tubing string for movement into frictional contact with a tubular member positioned in the well; each of said anchoring membershaving a hard smooth metallic surface for engaging said tubular member; and fluid pressureoperated means embodied in the' tubing string for urging vsaidfsurfaces ,of said anchoring members intoffrictional gripping contact with said tubular member forfrictionally Iholding the anchor-"with respect toftbfe` casing undennorrnal" stresses', andfor permitting sliding frictional movement of the` anchor relative tothe casing responsive to abnormal tubingstresses.

2. An anchor for. releasably restraining axial movement of a tubing string ina well, comprising: a tubular body adapted to be connected in a` tubing string; anchoring members mounted on said body for lateral movement relative thereto; each of said. anchoring members having a hard smooth metallic surface engageable with a tubular member in the well, and fluid pressure operated means on said bodyresponsive lto tluid pressure therein for urging said surfaces of'said anchoring members into frictional gripping'. contact with said tubular member for frictionally holding, the anchor with respect to the casing under normal stresses, and for permitting sliding frictional movement of theanchor relative tothe casing responsive to abnormal tubing. stresses. p

3. An anchor for releasably restraining axial movement of a tubing string ina cased wellpcompvriasing: anchoring members mounted on the tubing string.; for movement into frictional contactwith the casing' of the well; each of said anchoring members being exible and having a hard smooth metallic casing` engaging surface of'suhcient area to prevent biting thereof into said casing; and Huid pressure operated means on said tubing string responsive to fluid pressure in the string for. urging said surfaces of `said anchoring members Iagainst said casing for frictionally holding, the anchor` with respect to the casing under normal stresses, and forpermitting sliding frictional movement of the anchor relative to the casing responsive toV abnormal tubing stresses. Y

4l An anchor for releasably restraining axialmovement of a tubing string in'Aa cased well, comprising: anchoring members mountedl on the.l tubing string for movement into frictionalv contact with the casing of the well; each of said anchoring members'being resilient and having a-hardsmoothmetallic casing-engaging surface; and uidpressure operated means onsaidtubing` string responsive ,tol uid pressure insaidstring for urging said surfaces Vof said anchoring members into engagement -with said casing for frictionally-holding the anchorwith respect to the casing under normal'stresses, and foi-.permitting sliding frictional movement ofthe anchor. relative to the casing responsive to abnormal tubing stresses.

5. An anchor forrele'asably restraining axial movement of a tubing stringV in. a casedxwell, comprising: a tubular body adapted to be connectedin the tubing string; anchoring members mounted on said body for movement relative thereto; each of said .anchoring members being flexible and having a hardlsmootl metallic surface for frictionally engaging the well casing; cylinders on said body; said body having ports Whichopen into said cylinders; and pistons operable in said cylinders with their .outer ends in contact withsaid anchoring members for frictionally holding the anchor with respect tothe casing under normal stresses, andforpermittingl sliding frictional movement of the anchor relative to the casing responsive toy abnormal tubingstresses. g a

6. An anchor for releasably.` restrainingjaxial movement of a tubingv string vina casedwell, comprising: a tubular body adapted to be connected the tubing string; elongated flexible metallic anchoring members; means mounting said membersfon the exterior of said body for movement into frictional contact-with-the well 'surfaces said pistons being uid pressure operated for 'urging the anchoring members into frictional gripping contact with the casing, the anchoring members frictionally holding the anchor with respect to the casing under normal stresses and permitting sliding frictional movement of the anchor relative to the casing under abnormal stresses.

8. An anchor for releasably restraining axial movement of a tubing string in a cased well comprising: va tubular body adapted to be connected in the tubing string; elongated metallic anchoring members each having an effective portion between its ends providing a Ysmooth surface for frictionally contacting the well casing;

means on said body engaged with the ends of said members mounting said members for movement relative to said body; cylinders on said body; said body having ports which open into said cylinders; and pistons in said cylinders having their outer ends engaged with surfaces of said members opposite said casing contacting surfaces said pistons being uid pressure operated for urging the anchoring members into frictional gripping contact with the casing, the anchoring members frictionally holding the anchor with respect to the casing under normal stresses and permitting sliding frictional movement of the anchor relative to the casing under abnormal stresses.

9. An anchor for releasably restraining axial movement of a tubing string in a cased well comprising: a tubular body adapted to be connected in the tubing string; elongated metallic anchoring members each having an effective portion between its ends providing a surface for frictionally contacting the well casing; means iixedly mounting one end of each of said members on said body; means securing the other Vend of each of said members for axial movement relative to said body; cylinders on said body; said body having ports which open into lsaid cylinders; and pistons operable in said cylinders; said pistons contacting the surfaces of said members opposite said casing contacting surfaces saidpistons being fluid pressure operated for urging the anchoring members into gripping contact with the casing, the anchoring members holding the anchor with respect to the casing under normal stresses and permitting movement of the anchor relative to the casing under abnormal stresses. y

A10. An anchor for releasably restraining axial movement of a tubing `string in a cased well comprising: a tubular body adapted to be connected in the tubing string; metallic anchoring members mounted on said body for movement relative thereto; Said anchoring 'members being flexible and having smooth surfaces for frictionally engaging the Well casing; cylinders on said body; said body having ports which open into said cylinders; and pistons operable in said cylinders with their outer ends ,in contact with said anchoring members; the combined area of the portions of the pistons exposed to uid pressureginY said string being at least five times the internal cross sectional area of said string said pistons being fluid pressure operated for urging the anchoring members into-frictional gripping contact with the casing, the anchoring members frictionally holding the anchor with respect to the casing under normal stresses and permitting sliding frictional movement of the anchor relative to the casing under abnormal stresses.

11. A tubing anchor comprising: a tubular body adapted to be connected in a tubing string; means providing cylinders on said body; said cylinders opening into said body; `and pistons in said cylinders; said pistons having smooth surfaces for frictional engagement with a casing or tubular member in a well; each of said surfaces being of suicient area to prevent biting thereof into said casing or tubular member; the entire area of eachof said surfaces conforming to and being simultaneously engageable with the casing or tubular member. A'

l2. A tubing anchor comprising: a tubular body adapted to be connected in a tubing string; means providing cylinders on said body; ports in said body opening into said cylinders; and pistons in said cylinders having smooth outer ends for frictionally engaging a tubular member in a well; each of said outer ends having suicient area to prevent it from biting into said tubular member; the entire area of said ends being'simultaneously engageable f with and conforming to said tubular member.

i3. in a friction holding device foruse in wells: a tubular body adapted to be connected in a tubing string; means providing cylinders which. open laterally through the wall of the body; pistons in said cylinders movable outwardly responsive to iiuid pressure in said body; and means providing smooth metallic surfaces on said pistons for effecting a frictional holding action with a surface engaged thereby for frictionally holding the anchor with respect to the casing under normal stresses, and for permitting sliding frictional movement of' the anchor relative to the casing responsive to abnormal tubing stresses.

14. An anchor for releasably anchoring tubing string in a cased well comprising: a tubular body adapted to be connected in the tubing string; a plurality of piston and cylinder units carried by said body with the pistons movable laterally toward the casing of the well under pressure of uid in the tubing string; land a plurality of leaf spring members mounted on said body so as to straddle the outer ends of said pistons; said leaf spring members having hard smooth surfaces for frictionally engaging the well casing; said pistons being engaged with said leaf spring members at points opposite said surfaces; the pistons beingV uid pressure operated for urging the leaf spring members into frictional grippingv contact with the casing, said leaf spring members holding the anchor with respect to the casing under normal stresses and for permitting sliding frictional movement of the anchor relative tothe casing responsive to abnormal tubing stresses.

l5. An anchor for releasably holding a tubing string against axial movement in a cased well comprising: a tubular body adapted to be connected in the tubing string; a plurality of piston and cylinder units carried by said body with the pistons being movable toward the casing under the pressure of uid in the tubing string; a plurality of leaf spring members; means securing said spring members on said body; each of said spring members having a continuous smooth and hard surface extending axially thereof for frictionally engaging the well casing; each of said spring members being engaged at axially spaced points with pistons of said units; the pistons being fluid pressure operated for urging the leafspring members into frictional gripping contact with the casing, said leaf spring members holding the anchor with respect to the casing under normal stresses and for permitting sliding frictional movement of the anchor'relative to the casing responsive to abnormal tubing stresses.

16. An anchor for releasably anchoring tubing string in a cased well comprising: a tubular body adapted to be connected in the tubing string; a plurality of piston and cylinder units carried by said body with the pistons movable laterally toward the casing of the well under pressure of fluid in the tubing string; a plurality of leaf spring members mounted on said body so as to straddle the outer ends of said pistons; said leaf spring members having hard smooth surfaces intermediate their ends for frictionally engaging'the well casing; said pistons being engaged with said leaf spring members at points opposite said smooth surfaces; Vsaid pistons having slots therein; Vand stop pins extending through'said cylnders and said slots for limiting said lateral movement of said pistons; the pistons being liuid pressure operated for urging the leaf spring members into frictional gripping contact with the casing, said leaf spring members holding' the anchor with respect to the casing under normal stresses and for permitting sliding frictional movement of the anchor relative to the casing responsive to abnormal tubing stresses.

17. An anchor for releasably holding a tubing string against axial movement in a cased well comprising: a tubular body adapted to be connected in the tubing string; a plurality of piston and cylinder units carried by said body with the pistons being movable toward the casing under the pressure of liuid in the tubing string; a plurality of leaf spring members; means fixing one end of each of said spring members on said body and means mounting the other end of each spring member on said body for axial movement relative to said body; each of said spring members having a continuous hard and smooth metal surface extending axially thereof for frictionally engaging the well casing; the pistons of said units being engaged with said spring members opposite said surfaces; the pistons being iiuid pressure operated for urging the leaf spring members into frictional gripping contactwith the casing, said leaf spring members holding the anchor with respect to the casing under normal stresses and for permitting sliding frictional movement of the anchor relative to the casing responsive to abnormal tubing stresses.

18. An anchor for releasably anchoring tubing string in a cased Well comprising: a tubular body adapted to be connected in the tubing string; a plurality of piston and cylinder units carried by said body with the pistons movable laterally toward the casing of the well under pressure of uid in the tubing string; the pistons of said units each having a hard smooth surface for frictionally engaging the Well casing; ysaid pistons having slots therein; and stop pins extending through said cylinders and said slots for limiting said lateral movement of said pistons.

19. In a tubing anchor for anchoring a tubing string in a well casing, wherein anchoring means are forced into engagement with thecasing by uid pressure in the tubing, the anchoring means including a plurality of uid pressure responsive pistons: that improvement wherein the casing engaging surfaces of the anchoring means are constituted by smooth metallic surfaces, the iluid pressure operated pistons urging the anchoring means into frictional gripping contact with the casing, the anchoring means holding the anchor with respect to the casing under normal stresses but permitting sliding frictional movement of the anchor relative to the casing responsive to abnormal tubing stresses.

20. In a tubing anchor for anchoring a tubing string in a well casing, wherein anchoring means are forced into engagement with the casing by uid pressure in the tubing, the anchoring means including a plurality of uid pressure responsive pistons: that improvement wherein the casing engaging surfaces of the anchoring means are constituted by smooth metallic faces substantially conforming to the curvature of the casing, the iiuid pressure operated pistons urging the anchoring means into frictional gripping contact with the casing, the anchoring means holding the anchor with respect to the casing under normal stresses but permitting sliding frictional movement of the anchor relative to the casing responsive to abnormal tubing stresses.

21. An anchor as set forth invclaim 2 wherein the fluid pressure operated means include pistons, the anchoring members are elongated and straddle the outer ends of the pistons, and said outer ends are recessed for reception of said elongated members.

References Cited in the iile of this patent UNITED STATES PATENTS 2,133,462 McManS Oct. 18, 1938 `2,167,338 Murcell July 25, 1939 2,464,713 Penick Mar. 15, 1949 2,612,346 Nelson Sept. 30, 1952 2,658,459 Page Nov. 10, 1953 2,674,199 Page Apr. 6, 1954 2,674,313 Chambers Apr. 6, 1954 

